Short duration optical shutter



wilg 6 j" A u 2 3 3 E x 'ERENCE July 7, 1970 D. D. GROSSMAN SHORT DURATION OPTICAL SHUTTER Filed Nov. 20, 1967 Naoom 0.-. mmOa C. Om Z INVENTOR.

DAVID D. GROSSMAN nited States Patent O U.S. Cl. S50-150 5 Claims ABSTRACT F THE DISCLOSURE A short duration speed optical shutter having a lighttriggered spark-gap switch that activates a high voltage impulse generator to cause a Kerr cell to transmit up to 100% of incident polarized light for a duration that may 15 be adjusted from l to nanoseconds.

.SUMMARY OF THE INVENTION This invention was made in the course of, or under a contract with the United States Atomic Energy Commission.

This invention produces a high intensity, short duration light pulse with Kerr cell electrodes-forming a spark actuated high voltage pulser. In one embodiment the Kerr cell electrodes i -IE U v N Y that;lsmalamlatina-lishtetrisaetsslmsaads... a ...sa itc. himg an puteelsstmderumina parallel tiene missiolin'whereby application of the light trigger pulse to the spark gap switch energizes the transmission line so as`to open the Kerr cell fortraansmission of up to 100% It is a further object to provide a Kerr cell shutter system with the least interference with the transmission of incident light therethrough;

It is a still further object to provide a Kerr cell shutter system with an adjustable shutter speed of from 1 to 10 nanoseconds.

BRIEF DESCRIPTION OF THE DRAWING In the drawings where like elements are referenced alike, the figure is a partial schematic view of the Kerr cell shutter system of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the ligure, a Kerr cell 11 is shown having electrodes 13 and 15 adapted to hold a suitable/CIE;lszmnia` uid 1,7, for producing a Kerr eifect, which is we l known own by the systems described in Us. Pats. 3,169,163 and 3,164,665. A description of this well known Kerr effect is found in The International Dictionary of Physics and Electronics, D. Van Nostrand Co., Inc., 1956. One suitable dielectric tluid is rlitmbenzene, sincel it matches the dielectric constant of insulator 19, which is advantageously an acrylic resin plastic sheet. As is convenient, a lead 21 connecting the electrodes 13 and 15 includes a probe (not shown) to an oscilloscope. By suitably energizing the cell 11 incident light passes through electrodes 13 and 15 of cell 11 from lens 23 and polarizer 25 and through crossed polarizer 27 and lens 29 whereby the light retiected by test material 31 enters camera 33. The camera may, however, be mounted in any suitable locaof one polariiarireft' Hgf'legfedfatomgwaae'tion as below the test material. Also, the incident light nanoseconds or less. With the proper selection of elements, as described in more detail hereinafter, the desired short high intensity light pulse is obtained, e.g. in the range of from 1 to 10 nanoseconds.

BACKGROUND OF THE INVENTION ragaid for observation by conventiona means, such as 4 rotating mirror framing cameras, and in exploring the many stage interactions when light strikes matter with a short high intensity light pulse that doesnt destroy the matter. One system that has been employed for hydrodynamic research at elevated temperatures where high energy densities are accompanied by high particle and shock velocities, rapid phase transitions and the resulting small scaling of the physical events making interframe t'mies of less than 10-3 seconds desirable, has been the system described in U.S. Pat. 3,116,660. This system em- 5 ploys a Kerr cell shutter means, optical relay delay system means, and a microscopic or telescopic optical means for looking at the event and of forming images thereof. This system has the advantage that interframe time limitations are not imposed by the rotating mirror framing cameras known heretofore but by the Kerr cell and the synchronizing electronic circuits. Accordingly, it has been advantageous to provide a Kerr cell having fast electronic circuitry for hydrodynamic research. It has also been advantageous to provide a high intensity light pulse that is adjustable from 1 to 10 nanoseconds.

It is an object of this invention therefore, to provide a rapid acting Kerr cell shutter with a rapid acting actuating means for producing a short duration, high intensity light pulse for the non-destructive hydrodynamic study of test material;

may be directed through cell 11 at right angles to the as a1en"m1rizsr19m-fonfrfan1grvofr 37. Totlisgerdthe electrodes 13 and 15 and insulator 19 extend from Kerr cell 11 along insulat o r ^19v and terminate in a spark gap chamber 39"extending along an axis at right angles to the direction of the transmission line 35. The chamber 39 has a window 41 at one end for the transmission of a light impulse from source 43 therethrough for triggering the spark discharge of the high voltage direct current from input 45, resistor 47, lead 49 and a central electrode 51 mid-way between electrodes 13 and 15 to a V-shaped electrode 53 at ground potential. Advantageously, the chamber 39 is pressurized through pipe with a suitable ionizable gas, such as argon, while suitable gaskets 57, 59, 61 and 63 seal chamber 39 against the leakage of the gas pressure therefrom. This permits light source 43 to trigger the spark gap 63 formed between electrodes 51 and 53 for the spark discharge gap 63 so that a large direct current rapidly passes from input 45 through spark gap switch 65 of pulser 37.

In operation, the spark gap is pressurized to about 5 atmospheres so that its impedance is below that of the transmission line. Also, the length of the charged line provided by central electrode 51 for the spark gap 63 determines the duration of the high voltage pulse therein and hence the open time of the Kerr cell shutter 11. For the prototype, this time is 2 nanoseconds but this charge line 51 can be changed in length to provide adjustable pulse lengths from l to 10 nanoseconds long. Advantageously, the spark gap switch 65 is light triggered through window 41 by a laser pulse. A laser pulse is advantageous since it may be shorter than 1 nsec. For example, a conventional mode-lock laser puts out' a train of pulses that are about 1 picosec. long and are separated by a few nsec. Therefore, this device may 4 select a single piosecond light pulse. However, an ultratransmission through said Kerr cell by selectively changviolet flash source 43 may also be used. ing the location of said central conductor relative to said The output from pulser 37 caused by the spark distransmission line for changing the duration of time said charge across switch 65 travels a few inches down central transmission line is actuated by said light actuated spark electrode 51 and correspondingly produces a pulse in the gap switch when the latter is triggered by said light pulse parallel plate transmission line 35 provided lby electrodes thereto to conduct energy to said grounded end of said 13 and 15, which are terminated with a resistance 67 one electrode. equal to the 3. The invention of claim 1 in which said central conline 35. htteembdifref this resistance 67 is'v abii'tm ductor for causing a spark discharge in said spark gap SOQHand the Kerr cell extends perpendicglagr tgmth'ew ais' @o D switch when said'light triggered spark gap is liglit trg- `t`he transmission line 35.A i 'i gered, is selectively, adjustably located for operably ad- -The electrode 51 is force fitted into gasket 69 mid-way justing the actuation time of said spark gap switch. between electrodes 13 and 15 in insulator 19. Accordingly, 4. The invention of claim 1 in which the spark gap the distance this electrode extends into or beyond insulaswitch has a gas pressurized chamber forming an ,taxis at tor 19 is adjustable by merely moving this electrode 51 15 right angles to the direction of said spaced apart actuating inwardly or outwardly in gasket 69. To this end, portion electrodes, and said spaced apart actuating electrodes are 71 of electrode 51, which forms an annular gap 63 with at opposite ends of said chamber with said spa-'rk gap electrode 53, is biased through slit 73 between gaskets 59, switch mid-way therebetween which are sandwiched between portion 71 of electrode 51 5. In a Kerr cell having a dielectric uid, crossed polarand portion 75 of insulator 19 on one side of chamber 39. 20 izers, said Kerr cell located between said crossed polar- In thisregard, a small movement of the electrode 51 adizers, a light source, spaced apart, actuating electrodes justs the shutter speed of cell l1 from l to 10 nanoseconds connected to said Kerr cell, and means for energiz'ig said without appreciably affecting the operation of spark gap spaced apart actuating electrodes for causing said Kerr switch V65. If, however, electrode 53 needs adjusting, this cell to transmit light from said light source through said is accomplished by moving bar 77 on grounded bellows 25 Kerr cell and crossed polariaers, comprising gas contain- 79, which connects with electrode 53 and seals the bottom ing, spark gap means, and light trigger means for actuof chamber 39. This bellows 79 also resiliently absorbs ating said spark gap means to produce a spark discharge any spark induced expansion of the gas in chamber 39 for energizing said actuating electrodes for causing said while maintaiinng the desired position of electrode 53 Kerr cell to transmit Said light, the improvement, com. for the Sequential llrihg f Switch 65 and the reSUltnt 30 prising parallel plate transmission line means having first opening and closing of cell 11. and second, parallel, spaced apart plates connected While this invention has been described aS Supplying a through a resistance at one end to form said spaced apart high ihehSilY, Short duration light pulse, it is also underactuating electrodes, and forming one opposite free end, stood that it can also operate simply as a camera shutter and one grounded end for connecting said spark disfgiphotographing a process carried out at high bright-v charge to said spaced apart actuating electrodes and said ness. In this case, the camera is suitably placed at one side Kerr eell for actuating the same for utilizing 'the full of the cell 11 of this invention to receive light producing voltage of said spark discharge for actuating said Kerr ah image that Passes throllgh the cell Wheh ii iS operi. cell to transmit said light, a longitudinally extending in- This invention has the advantage of providing pracsulator interposed between said first and second, parallel,

tical and effective system for producing Short, high in- 40 spaced apart plates along a portion of the length of said tensity light pulses for hydrodynamic research, high speed plates, and interposed between said dielectric uid and Photography 01 other PUYPoSeS Where Such PUlSeS are errlsaid spark gap means at the opposite ends of said insulaployed ih ihe hoh-destructive eSilhg of materials. The tor, and central conductor means extending selectively adsystem of this invention, for example, is adapted t0 prO- justably in a portion of said insulator from one end thereduce light pulses between 5 and 50 million watts for 2 45 of intermediate said plates, parallel therewith, terminatnanoseconds or less. Moreover, the system of this invening at a distance from Said Kerr eell and having a high iioh Seleciivcly ProvideS ah easy, ellecilve, and opel'ahly voltage source for producing a spark dischargeproducadjustable system for producing high intensity light pulses ing potential in said spark gap means for producing said from 1 to l0 nanoseconds in duration. spark discharge when said spark gap means receives a What is claimed is: light trigger pulse from said light trigger means,'said cen- 1- A Short duration, high ihiehSily optical Shutter, comtral conductor being adjustable for changing the, location PlSiDg the Combination 0f a light SOUree, crossed polarof said central conductor relative to said spark gap means izers, a Kerr cell having a dielectric uid located between for changing the time duration during which said spark said polarizers and resistance connected, spaced apart, discharge energizes said actuating electrodes for changactuating Clectl'OdeS forming a parallel plate tlallSmlSSlOIl 55 ing [he time duration during which said Kefrccl] and line for applying an electric tielglacrpssmsaidwlggrmgll polarizefs transmit light from said light source. wherein one electroderforms. `gngrovunled end and an end which is'connected by said resistance, and said other elec- References Cited trode forms an end connected by said resistance and an UNITED STATES PATENTS opposite free end, and means having a light triggered spark `gap switch forming a central conductor in a p0r- 3,041,936 7/1962 Hull .-7 350-150 tion of said parallel plate transmission line for causing a 3,295,012 12/1966 Barhlrll 315-149 spark discharge in said spark gap when said Spark gap re- 3,432,664 3/1969 Robison 25o-98 ceives a light trigger pulse for conducting said spark discharge to the grounded end of said one electrode for FOREIGN PATENTS actuating said transmission line during a short period of 1 456 884 9/1966 France" time for selectively causing said spaced apart actuating electrodes to open and closle said Kerr tclell fo;l thedtins- D AVID SCHONBERG, Primary Examiner mission of li ht from said ight source roug sai `err cell for prodgucing a short, high intensity light pulse.A P- R- MILLER Asslsiam Examiner 2. The invention of claim 1 in which said central con- U S Cl X R ductor has a power source and is operably, adjustably,

and selectively located midway between said spaced apart -53; Z50-199; 350-160 actuating electrodes for adjusting the duration of said light 

